1. Field of the Invention
The present invention is broadly concerned with stable starch products including respective quantities of resistant starch and at least one hydrocolloid interacted with the starch. These products exhibit increased dietary fiber content, resistance to α-amylase digestion, and confer enhanced emulsion stabilities, and hot and cold water swelling capacities, in water-oil and other aqueous systems, and are particularly suited for use in food.
2. Description of the Prior Art
It is well known that certain types of starches are resistant to human pancreatic α-amylase digestion and provide the health benefits of dietary fiber upon ingestion. As a consequence, considerable research has been conducted to provide resistant starches of various types and modifications thereof.
In 1987 Englyst and Cummings at the MRC Dunn Clinical Nutrition Center in Cambridge, UK, proposed a classification of starch based on its likely digestive properties in vivo. They also devised in vitro assay methods to mimic the various digestive properties of starch. Three classes of dietary starch were proposed:
(1) Rapidly Digestible Starch (RDS). RDS is likely to be rapidly digested in the human small intestine; examples include freshly cooked rice and potato, and some instant breakfast cereals.
(2) Slowly Digestible Starch (SDS). SDS is likely to be slowly yet completely digested in the small intestine; examples include raw cereal starch and cooked pasta.
(3) Resistant Starch (RS). RS is likely to resist digestion in the small intestine. RS is thus defined as the sum of starch and starch degradation products not likely to be absorbed in the small intestine of healthy individuals. RS can be subdivided into four categories depending on the causes of resistance (Englyst et al 1992; Eerlingen et al 1993).
RS1. Physically inaccessible starch due to entrapment of granules within a protein matrix or within a plant cell wall, such as in partially milled grain or legumes after cooling.
RS2. Raw starch granules, such as those from potato or green banana, that resist digestion by α-amylase, possibly because those granules lack micropores through their surface.
RS3. Retrograded amylose formed by heat/moisture treatment of starch or starch foods, such as occurs in cooked/cooled potato and corn flake.
RS4. Chemically modified starches, such as acetylated, hydroxypropylated, or cross-linked starches that resist digestion by α-amylase. Those modified starches would be detected by the in vitro assay of RS. However, some RS4 may not be fermented in the colon.
RS1, RS2, RS3 are physically modified forms of starch and become accessible to α-amylase digestion upon solubilization in sodium hydroxide or dimethyl sulfoxide. RS4 is chemically modified and remains resistant to α-amylase digestion even if dissolved.
Numerous methods have been disclosed for the production of various types of resistant starches. Raw granular starches with B-type crystallinity (RS2) based upon high-amylose (more than 50%) corn starches are disclosed in U.S. Pat. Nos. 5,977,454, 6,451,367, 6,409,840, 6,303,174, and 5,977,454. U.S. Pat. Nos. 5,593,503 and 6,664,389 describe methods for producing resistant starches employing specific combinations of heat and moisture with high-amylase corn starches. Other references, including U.S. Pat. Nos. 5,281,276, 5,409,542, 7,081,261, and 6,013,299 disclose methods for preparing non-granular, retrograded resistant starches, mainly based upon high-amylose starches, while U.S. Pat. Nos. 6,043,229 and 6,090,594 describe retrograded resistant starches made from tuber and non-high-amylose starches. Finally, U.S. Pat. Nos. 5,855,946 and 6,299,907, as well as U.S. published application 2006/0188631 disclose methods to produce resistant starches by appropriate cross-linking, using virtually any type starting starch material.
Interaction between starch and hydrocolloids have long been known and reported by many researchers. Fanta et al. prepared starch hydrocolloid composites by a jet cooking and drum drying process (Food Hydrocolloids, 1996 10 (2), 173-78), and showed that the products have physical properties different from those obtained by conventional cooking procedures, and suggested that the products be used in food systems as fat replacers, stabilizers, gelling agents, and thickeners. Shi et al. reported the effects of gum addition on pasting properties of starches and suggested that the interaction between leached amylose molecules and certain gums was responsible for viscosity increases before starch pasting (Carbohydrates Polymer, 2002 50; 7-18). Lim et al. (Cereal Chemistry 2002 79 (5), 601-06) found that dry heating of anionic gums with starch altered pasting properties depending upon the combination of starch and gum used.
However, the prior art does not address or suggest interaction products made from resistant starches and hydrocolloids, or any resulting nutritional or functional benefits.